Although the variety of dyes and pigments known in the art is very wide, there is a continuing effort by synthetic dye chemists to discover new chromophoric systems for use as colorants in a broad range of applications. These applications include: textile dyes, hair dyes, paint pigments, printing inks, inkjet colorants, rubber and plastic colorants, polymer stabilizers, electrochromic and thermochromic display devices, laser dyes, electrophotographic pigments, sensitizing dyes, image dyes, and filter dyes for photographic systems, liquid crystal display devices, optical disks, biological stains, and others.
A wide variety of dyes are employed in photographic materials. In addition to the diverse dyes used to form images in color photographic elements, spectral sensitizing dyes are used to extend the sensitivity of silver halides, which are inherently sensitive only to blue light, to other wavelengths of radiation. Among the dyes commonly employed for this purpose are the cyanines and merocyanines, which are discussed in T. H. James, ed., The Theory of the Photographic Process, 4th Ed., Macmillan, N.Y., 1977, Chapter 8, and in F. M. Hamer, Cyanine Dyes and Related Compounds, Wiley, N.Y., 1964.
Photographic materials often contain filter dyes to absorb light from different regions of the spectrum, such as red, blue, green, ultraviolet, and infrared, to name a few. These filter dyes are often required to perform the function of absorbing light during exposure of the material so as to prevent or at least inhibit light of a specific spectral region from reaching at least one of the radiation sensitive layers of the element. Dyes are also used in color photographic materials as filters, typically located in overcoats or interlayers, to absorb incident radiation and improve image sharpness. It is a particular problem that many polymethine dyes used as intergrain absorbers in photographic films are fluorescent, and upon absorbing light at their absorbance maxima can in turn emit light in the form of fluorescence, generally at a wavelength longer than that of their absorbance maxima. Fluorescence by absorber dyes can result in false sensitization of sensitized emulsions, rendering some classes of dyes unfit for use in photographic materials.
In addition, dyes are often used in non-imaging layers as antihalation dyes which absorb the radiation that passes through the imaging layers unabsorbed, and hence prevent undesirable blurriness of the final image. After processing of the element, however, the continued presence of the antihalation dye will adversely affect the image quality of the photographic material. It is therefore desirable to use antihalation dyes that will be solubilized and removed or at least decolorized during photographic processing. Dyes that are easily solubilized, however, tend to wander throughout the photographic material during coating, adversely affecting the final image quality. To prevent dye wandering, the dyes can be coated with a mordant to bind the dye in the layer in which it is coated. Dye mordants, while often useful, tend to either bind the dye too strongly, inhibiting solubilization of the dye during photographic processing, or too weakly, thus not preventing dye wandering. To address this problem, dyes used as antihalation dyes or filter dyes may be formulated a solid particle dispersions. Solid particle dispersions allow for the coating of filter dyes in a layer-specific manner such that the dyes are immobile in coated acidic emulsion layers, but then are fully removed in the high pH environment of photographic processes. Solid particle dispersions of highly stable dyes also offer advantages for use in output media such as inkjet printing.
There are numerous patents describing various filter dyes formulated as water-soluble absorber dyes or as solid particle dispersion dyes, for example, U.S. Pat. Nos. 4,950,586; 4,948,718; 4,948,717; 4,940,654; 4,923,788; 4,900,653; 4,861,700; 4,857,446; and 4,855,221. Further, some nuclei represented generally by Formula I below (X═SO2, C═O; Y═S2, C═O) are known; specifically the benzothiazine compounds described by Formula IA below are described in (Lombardino et. al.; Org. Prep. Proc. Int. 1971, 3(1), 33) and (U.S. Pat. No. 3,303,191). Tautomeric derivatives substituted at the ketomethylene position by various ester groups are also described for pharmaceutical applications (JP 46022150). However, none of these references describe any polymethine or azamethine dyes derived specifically from the benzothiazine nuclei utilized in the current invention, or other closely related nuclei, or their use in imaging elements.
Regardless of the large number of known dyes, there is still a need in the imaging arts for filter dyes which do not fluoresce and which can be used as absorber dyes or antihaltion dyes.